We need an actual picture of WK-4 and not a drawing.
If anyone is a member of oldgmc trucks, or owns an original GMC, it would be helpful to get a picture for comparison.
Unfortunately for me, I have tried to register but was denied. They may require ownership of a GMC.

"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."